The present invention relates to differential transformers and in particular to a linear variable differential transformer whose output is not influenced by temperature variation.
Differential transformers of the type composed of a bobbin of nonmagnetic, nonconductive material, and having primary and secondary coils wound thereon with a displaceable magnetic armature core, the position of which determines the number of secondary coils magnetically coupled with the primary coil are well known. Such devices are disclosed, for example, in U.S. Pat. No. 3,376,533 and are widely used to measure linear displacement.
In low frequency applications a high proportion of the impedance of the transformer comprises the resistance of the coils. The resistance is temperature sensitive and therefore the output of the transformer will be affected by ambient temperature. As noted, the effect is more prominent as the frequency of the exciting voltage decreases. This may create a problem in many applications especially where a small displacement of the armature is sought to be detected and the operating voltage is low frequency (i.e., 400 Hz or less).